In a propeller assembly including a propeller hub supporting a plurality of radially projecting adjustable pitch propeller blades, for example, of the general type disclosed in U.S. Pat. Nos. 4,097,189, 4,650,402, 4,699,568 and No. 4,904,157, it is common for the propeller blades to carry electrical heating elements or boots for preventing the build up of ice on the blades. Electrical power at a predetermined voltage, such as 28 Volts DC, is supplied to the electrical heating elements or boots mounted on the blades through concentric slip rings mounted on a radially disposed bulkhead secured for rotation with the propeller hub. The rotating slip rings contact non-rotating corresponding brushes, and the slip rings are electrically connected to the heating element or de-icing boot on each of the propeller blades by a pair of flexible wires or leads. The inner ends of each pair of leads include terminals which are releasably secured by screw fasteners to corresponding terminal blocks mounted on the forward face of the bulkhead, and a removable plug connects the outer ends of each pair of lead wires to a mating socket at the base portion of the propeller blade.
As the pitch of the propeller blades changes during operation of the aircraft, the leads extending from the slip rings to the propeller blades are required to flex. Commonly, the leads are each constructed of stranded copper wires tightly surrounded with an insulation material including multiple layers of braided cotton or synthetic fibers. Each pair of insulated copper wires may also be tightly covered with a tube of rubber or Neoprene insulation material. However, when these insulated copper wires flex with blade pitch changes, concentrated stresses and metal fatigue develope within the wires, with the result that at least a portion of the copper wires break after an extended period of use. Thus the wires or leads must be frequently inspected and tested and if wires are broken, must be removed and replaced with new leads, all of which adds to the down time of the aircraft and to the cost of maintaining the aircraft.